Along with development of telecommunication technologies, the traditional Public Switched Telephone Network (PSTN), primarily oriented to circuit switching, is in gradual transition to the Next Generation Network (NGN), primarily oriented to packet switching. Transmission in the packet network is based on Internet Protocol (IP)/Asynchronous Transfer Mode (ATM), which can unload a large amount of data in the PSTN network into the IP network to alleviate a heavy burden on the PSTN network. Furthermore, the packet network can add numerous new services or enhance old services with the use of new features of IP technologies, thereby making it possible to realize convergence of voice, video, data services, etc., over the communication network.
In communication over the packet network, media resource control is required during establishment of a call connection, switching of a service, etc. For example, both transmission parties need to negotiate about media capabilities prior to transmission of a media stream so as to obtain information of each other's reception addresses, codec (coding and decoding) types, etc. Existing media resource control methods primarily perform based upon destination attributes of media of both transmission parties. Taking the H.248 protocol in popular use as an example, the H.248 protocol defines the Local descriptor carrying destination attributes of locally received media and the Remote descriptor carrying destination attributes of locally transmitted media. The destination attributes of media carried in the Local and Remote descriptors are bearer-dependent and typically include an IP address, a port number, a codec type and parameters thereof, etc., of locally received media, for example, in the case of an IP bearer. The Local and Remote descriptors reflecting received media capabilities and attributes of both call parties are reported in messages to a Media Gateway Controller (MGC) through a Media Gateway (MGW) to which the user belongs, and are sent via the MGC to exchange media resource capabilities.
In the above media resource control method, since the Local and Remote descriptors only relate to destination attributes of media of both transmission parties, if destination attributes of media provided from a termination are inconsistent with source attributes, for example, if the termination is provided with a video display capability but without a video transmission capability, or if different addresses are used for transmitted and received media, then it is difficult to notify the remote end through negotiation in the existing control method. Further to basic call establishment, an IP termination with use of the Real-Time Transport Protocol (RTP) or another protocol on the belonged MGW has to process all of received packets consistent with its destination attributes of received media, without distinguishing between an attacking IP packet and an legal IP packet; and if attack IP packets or trash IP packets are attacking, then a large amount of system resources have to be occupied to process, such IP packets. For a reception termination of a unidirectional media stream, the reception termination also has to process a media stream originating from other transmission termination than the unidirectional media stream transmission termination upon reception thereof; thus, wasting system resources.